Energy Reducing Retrofit Apparatus For A Constant Volume HVAC System

ABSTRACT

An energy-reducing method and apparatus for retrofitting a single zone, constant volume HVAC system, with or without an economizer, that provides heating, cooling, and ventilation to occupants within a building space. The present invention includes the introduction of a programmable logic controller and variable frequency drive (VFD) that takes control of the existing fan, heating, cooling, and optional economizer operation. The reduction of the fan speed in the ventilation mode when the 100% operation is not needed saves significant energy of the existing constant volume HVAC system where the fan motor is designed to run 100% of the time.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/899,916, filed Feb. 20, 2018 entitled “Energy Reducing RetrofitApparatus For A Constant Volume HVAC System,” which is a continuation ofco-pending U.S. patent application Ser. No. 14/689,344, filed Apr. 17,2015 and which issued as U.S. Pat. No. 9,933,178 entitled “EnergyReducing Retrofit Apparatus for a Constant Volume HVAC System,” which isa divisional of U.S. patent application Ser. No. 14/563,941, filed Dec.8, 2014 and which issued as U.S. Pat. No. 9,043,034 entitled “EnergyReducing Retrofit Method and Apparatus for a Constant Volume HVACSystem,” which is a continuation of U.S. patent application Ser. No.13/920,331, filed Jun. 18, 2003 and which issued as U.S. Pat. No.8,965,586 on Feb. 24, 2015 entitled “Energy Reducing Retrofit Method andApparatus for a Constant Volume HVAC System,” which is a continuation ofU.S. patent application Ser. No. 12/544,960, filed Aug. 20, 2009 andwhich issued as U.S. Pat. No. 8,515,584 on Aug. 20, 2013, entitled“Energy Reducing Retrofit Method for a Constant Volume HVAC System.”

TECHNICAL FIELD

The present invention relates to energy saving improvements to constantvolume HVAC systems, particularly, the invention relates to the retrofitmethod and apparatus in order to control and reduce energy consumptionthrough the use of an efficiency enhancing controller, a variablefrequency drive, fault detection, and an optional occupancy sensor.

BACKGROUND OF THE INVENTION

HVAC (Heating, Ventilation, & Air Conditioning) systems are used to meetoccupant comfort and ventilation needs within a building space.Typically this involves the conditioning of air circulated to and fromthe space served via an air handler of some form, e.g., fans andblowers. Conditioning the air can include any combination of heating,cooling, filtering, humidifying, & dehumidifying air in a definedbuilding space. Additionally, most HVAC systems have provision forsupplying minimum amounts of fresh outside air to insure properventilation for human occupants.

HVAC systems include constant volume systems and variable volumesystems. Variable volume systems tend to be larger in capacity andgenerally more sophisticated in terms of control features. Constantvolume rooftop packaged units and split systems equipped witheconomizers are much more common than variable volume systems. Enhancedfeatures are rare in these systems due to cost considerations. Constantvolume systems, as their name suggest, deliver a constant volume of airto the building. Moreover, constant volume systems typically serve asingle zone or segregated space within a building.

The operation of these systems typically involves a room thermostatcontrolling the heating, cooling, and ventilation modes based on whetherthe space is occupied and the programmed heating and cooling set points.Whenever a non-residential space is open for business or has workers inthe facility, the space is considered to be in the “Occupied Mode.” In aconstant volume system, the HVAC system's fan is commanded to operate atfull capacity and the economizer provides minimum outside air foroccupant ventilation throughout the occupied workday without regard tothe temperature of the outside air. Changes in space temperature resultin the thermostat sending commands to heat or cool the air beingsupplied to the space as necessary. The total amount of energy requiredto heat or mechanically cool the air is impacted by the temperature ofthe outside air entering the system. The colder the outside air isrelative to the space, the greater the amount of energy required to heatthe air. The hotter the outside air is relative to the space, thegreater the amount of energy required to cool the air.

In virtually all constant volume systems the amount of outside airsupplied to the space for ventilation is set for the maximum number ofpotential occupants anticipated in the space. For instance, a restaurantmay have a dining room rated for 50 occupants. In this case, the HVACsystem's minimum outside air setting will be based on the code requiredventilation rate for 50 occupants. However, the dining room served bythis HVAC system may only have 50 occupants at peak business hours or onrare occasions. The result is an over-ventilated space whenever thereare less than 50 occupants. As stated previously, there is an energycost associated with heating or cooling outside air. The status quoapproach to occupant ventilation with these systems results inunnecessary energy usage.

Constant volume HVAC systems typically operate indoor blower motors atfull capacity throughout the occupied period. The reality is that thefans do not need to operate at full capacity. Manufacturers provide arange of operation for acceptable airflow in the heating and coolingmodes. A fan at full capacity typically exceeds the minimum allowablerequirements. The ability to properly ventilate the space does notrequire the fan to be operated at 100 percent airflow. Once again thesesystems are not equipped with the ability to reduce fan speed and airvolume in response to the true needs of space.

Sophisticated variable volume systems are able to vary the volume of airbased upon the needs of the space. This can be achieved via oldertechnologies such as inlet guide vanes or discharge dampers.Increasingly, variable volume systems rely on Variable Frequency Drives(VFD) for fan control. A VFD directly controls the speed of the fan andthe air volume by reducing the motor revolutions per minute (RPM). Fanaffinity laws prove that a 10% reduction in air volume or flow equals a27% reduction in energy usage. This exponential energy dividend makesVFDs a highly valued energy efficiency tool. Once again, the cost of theVFD and the associated sensors, wiring, and installation labor has madethe prospect of applying this technology to simple systems impractical.Additionally, the industry prior art has failed to identify a controlstrategy for applying variable volume technologies to retrofit a systemdesigned to move a constant volume of air.

Constant volume systems are able to respond to the impact of changes inoccupancy levels as they affect temperature, but they have no ability torespond to the varying ventilation needs associated with changingoccupancy levels. For this to occur, these systems must have moreintelligence and dynamic control capability.

Constant volume systems generally come in two distinct HVAC systemtypes: rooftop packaged units and split systems. Rooftop packaged unitsare typically self-contained units mounted on a roof. Split systemstypically include two sections: an indoor air handler/heating sectionand an outdoor compressor section connected to each other withrefrigerant piping. Many of these systems are equipped with economizers.An economizer consists of mechanically-actuated outside air and returnair dampers, temperature/humidity sensors, and an economizer controller.These components act together in such a way as to vary the amount offresh outside air introduced by the HVAC system into the building space.The primary purpose of an economizer is to allow the HVAC system toutilize outside air for “free cooling” in the event that the spacerequires cooling and the outside air is suitable to be used as a sourceof cold air to cool the space. This allows the HVAC system to avoid theexpense of operating the air conditioning compressor to make cold air.

Economizers are effective at lowering energy consumption if they arecontrolled properly and in good working order. Many studies by variousutilities, energy consulting groups, and professional organizationsreport that 60-80% of economizers in the field are not working properly.Even properly working economizers often lack appropriate limitations ontheir operation when the HVAC system is operated during the unoccupiedperiod (morning warm-up or night setback). Constant volume HVAC systemsoperate the economizer whenever the fan operates even though is notnecessary to ventilate an unoccupied space. The most common flaw as itrelates to ventilation during the occupied period is the improperpositioning of the outside air damper resulting in an over-ventilatedcondition.

In larger, variable volume HVAC systems, one strategy to address this isthrough “Demand Control Ventilation” (DCV). The benefit of DCV isderived from being able to position the outside air damper to a closedor nearly closed condition unless there is a measured need foradditional fresh air to the space. This is achieved by the use of anoccupancy sensor. While other mechanisms may exist for calculating theoccupancy level of a building, monitoring carbon dioxide levels is themost common. In such a case, a carbon dioxide (CO₂) sensor is mounted inthe building space or in the return air duct. Human occupants exhalecarbon dioxide and an increase in the number of occupants will produce acorresponding increase in the CO₂ levels. A controller is used tomonitor the CO₂ levels and modulate the outside air damper open asnecessary to dilute the CO₂ levels with fresh air. This dynamic approachto ventilation control eliminates the problem and energy expenseassociated with over-ventilating that comes with conventional strategiesbut has only rarely been applied as a retrofit measure with constantvolume systems and not with ventilation fan reduction and/orheating/cooling fan reduction.

A traditional economizer in a constant volume HVAC system uses outsideair for free cooling as an alternative to mechanical cooling compressoroperation. The economizer controller determines the operation of theeconomizer by referencing the temperature and/or humidity of the outsideair. When the thermostat communicates a call for cooling to the HVACsystem, the economizer controller determines if the outside air issuitable for free cooling. If so, the outside air damper is modulatedopen and mechanical cooling is held off. The point at which thistransition occurs is referred to as the “changeover point.” If theoutside air is not suitable, the economizer controller keeps the outsideair damper in the minimum ventilation position and commands thecompressor on for mechanical cooling.

In larger, variable volume HVAC systems, an “integrated economizer”strategy is implemented. This allows the simultaneous use of thecompressor for mechanical cooling and outside air economization. The useof outside air may not be suitable for meeting the total cooling loadbut can still work to lower the energy consumption of the system.Whereas traditional economizer logic allows either the compressor ORoutside air to function, an integrated economizer allows both tofunction together. Constant volume systems rarely include integratedeconomizer operation, but again not with the combination of ventilationfan reduction and/or heating/cooling fan reduction.

The most common style of changeover sensor is a “dry bulb” sensor. Thisis simply the measured sensible temperature of the outside air. A commondry bulb changeover temperature range is 55-60 degrees Fahrenheit. Drybulb sensors are most prevalent because they are the lowest costsolution.

In areas where humidity is a particular concern, “enthalpy” changeoveris often preferred. Humidity contains heat that cannot be measured by adry bulb temperature probe or sensor. For this purpose, an enthalpysensor is required. Enthalpy is a measurement of the “total” heat in theair and is measured in BTUs/lb of air. By using enthalpy control, thesystem more accurately assesses the suitability of outside air for freecooling. Optimizing the use of outside air for free cooling ultimatelyreduces the energy use of these HVAC systems.

Regardless of the changeover sensor used, any static changeover setpointwill fail to achieve the highest optimized condition when it comes tofree cooling. While enthalpy does allow for better control of aneconomizer there are additional strategies available for improvingenergy usage. One of these strategies is known as “differentialeconomizer control” and involves the use of two sensors. One sensorreferences the condition of the outside air and the other sensorreferences the condition of the return air from the space. Differentialeconomizer control compares both sensors and decides if it is moreadvantageous to mechanically cool return air from the space or outsideair. This strategy results in improved energy efficiency though is nottypically used in constant volume systems due to cost considerations.

It is reported that approximately half of all U.S. commercial floorspace is cooled by self-contained, packaged air-conditioning units, mostof which sit on rooftops. The energy saving potential from optimizingthe economizer, ventilation, and fan operation of these HVAC systems isenormous.

SUMMARY OF THE INVENTION

The invention works to solve many of the issues presented above byproviding an enhanced programmable logic controller with a variablefrequency drive capability to retrofit an existing constant volume HVACsystem and mimic the efficiencies inherent in more sophisticated HVACsystems. By controlling the speed of the fan motor (and ergo the fan) tobetter match occupancy needs, the fan motor can be run at asignificantly reduced speed in the ventilation mode. Controlling thespeed of the fan motor (and ergo the fan) to maintain minimummanufacturer recommended airflow levels during the heating and coolingmodes also provides a reduction in motor speed. Such reductions in thefan motor speed reduces current draw and, therefore, provide significantenergy savings over prior art constant volume HVAC systems.

The method of retrofit provides a programmable logic controller andoperably connects it to an existing thermostatic device and to existingheating and cooling equipment terminals. A variable frequency drive(VFD) that is controlled by the enhanced programmable logic controlleris operably connected to an existing fan motor, itself connected to theexisting HVAC fan.

The method of retrofit reduces the speed of the fan motor in theventilation, heating and cooling modes.

The method of retrofit may further include demand control ventilation(DCV), in which an occupancy sensor (e.g., a Carbon Dioxide CO₂ sensor)is added to measure occupancy levels of the building space controlled bythe HVAC system. CO₂ sensing is currently the most common measurementfor determining occupancy levels within a space. The CO₂ sensor sendsits sensed occupancy level to the controller. The controller modulatesthe speed of the fan motor (and ergo the fan) and the outside air damperposition to match the needs of the space. The outside air damper iscontrolled by and operably connected to the enhanced programmablecontroller.

Further, the controller may also control a constant volume system thatincludes an economizer. The enhanced programmable logic controller isoperably connected to an economizer actuator that operates the outsideair and return air dampers in response to one or more sensors. Theeconomizer sensor(s) may sense dry bulb air temperature, or enthalpy, ordew point.

According to other aspects of the present invention, additional energysavings may be further achieved through integrated economization,differential economizer control, and unoccupied damper control.

The method of retrofit may include “integrated economizer” where theenhanced programmable controller allows simultaneous mechanicalcompressor cooling and economizer free cooling operation to meet thecooling demand of the space.

The method of retrofit may include “differential economizer control” inwhich outside air and return air sensors are monitored and measured todetermine the preferred source of air for cooling operations.

The method of retrofit may include “unoccupied damper control” in whichthe outside air damper is kept closed during the unoccupied heatingmodes, such as morning warm-up.

The enhanced programmable logic controller and VFD may be combined in asingle efficiency enhancing controller (EEC) unit that can be readilyadapted to an existing constant volume system without great expense orintrusion.

The method of the present retrofit invention, and related EEC apparatus,can reduce the fan speed by up to 80% depending on occupancy demands ofthe building space.

The method or apparatus may be used in a stand alone or networkedversion.

The method or apparatus of the present invention may be further enhancedwith a networked version of the EEC and also include a fault detectioncapability. This enhanced embodiment may include a discharge air sensor,a current status switch, and a wireless transmitter.

These and other advantages will become more apparent upon review of theDrawings, the Detailed Description of the Invention, and the Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Like reference numerals are used to designate like parts throughout theseveral views of the drawings, wherein:

FIG. 1. is a schematic diagram of a prior art single zone HVAC constantvolume system illustrating a fan and fan motor, heating, cooling, andeconomizer dampers;

FIG. 2. is a schematic diagram illustrating an aspect of the energysaving HVAC system of the present invention in which an energyefficiency controller (EEC) is connected to an existing thermostaticdevice and takes control of the fan, cooling, and heating operations ofthe existing constant volume HVAC system;

FIG. 3 is a schematic diagram illustrating an alternate embodiment ofthe energy saving HVAC system of the present invention in which anenergy efficiency controller (EEC) takes control of the fan, economizerdampers, cooling and heating operations of the existing single zone HVACconstant volume system and adds occupancy based ventilation sensing andcontrol capabilities (DCV);

FIG. 4 is a schematic diagram illustrating another alternate embodimentof the energy saving HVAC system of the present invention in which anenergy efficiency controller (EEC) takes control of the fan, economizerdampers, cooling and heating operations of the existing single zone HVACconstant volume system and adds occupancy control as well as sensor andcontrol capabilities related to the economizer;

FIG. 5 is schematic diagram illustrating installation of an energyefficiency controller (EEC) across an existing thermostatic device andHVAC equipment terminals and controlling the fan motor;

FIG. 6 is a front view of an exemplar unitary EEC of the presentinvention;

FIG. 7 is a logic chart illustrating the controller inputs and outputsof the present invention;

FIG. 8 is a logic chart illustrating the fan or ventilation mode ascontrolled by the EEC;

FIG. 9 is a logic chart illustrating the cooling mode as controlled bythe EEC;

FIG. 10 is a logic chart illustrating the heating mode as controlled bythe EEC;

FIG. 11 is a logic chart illustrating the economizer mode as controlledby the EEC;

FIG. 12 is a logic chart illustrating fault data storage and detection;

FIG. 13 is a logic chart illustrating additional fault detectionmethods;

FIG. 14 is a schematic diagram illustrating a networked version of thepresent invention;

FIG. 15 is a schematic diagram illustrating a network layout; and

FIG. 16 is a mixed air temperature chart.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method and apparatus forsignificantly reducing energy consumption of an existing constant volumeHVAC system with or without an economizer. In a constant volume HVACsystem the fan runs continuously at the same speed, and the volume ofair being supplied to the space does not change (constant air flowrates). A thermostatic control device (most commonly a thermostat)controls the heating and cooling operations. Economizers are thearrangement of dampers that control the quantity of return air (aircoming back from the space being treated) and outside air (fresh airbeing used for cooling or ventilation). Here, the invention involvestaking control over the existing fan, cooling, and heating operation,and optional economizer of the existing system.

In contrast to a constant volume system, a variable air volume system(VAV) relies on the reduction of air flow or fan motor speed (and ergofan speed) to attain energy savings. However, variable air volumesystems by their nature have a stable supply-air temperature, are morecomplex, expensive, and generally used for larger commercial buildings.The present invention retrofits a constant volume HVAC system and mimicsthe energy saving features of a variable air volume system but withoutthe complexity and expense.

Referring to FIG. 1, a prior art schematic of the key components of aconstant volume

HVAC system are illustrated. The prior art constant volume HVAC systemsmay have many components but in general having a fan assembly (fan 10.3,fan motor 9.4, blower), heating equipment 10.4, cooling equipment 10.5,a thermostatic device, means for delivering treated air to a specificbuilding space, and means to control the temperature needs in aparticular building space and to operate the fan motor, coolingequipment, and heating equipment when ventilation, cooling, or heatingis requested. Some constant volume systems also include economizerdampers 10.1 to allow outside air into the system. As discussed above,the prior art system is not sophisticated and runs the fan at 100%capacity regardless of the call for heating, cooling, or ventilationneeds. This system lacks optimum efficiency.

Now referring also to FIGS. 2-6, the present invention is a method andapparatus for retrofitting an existing constant volume HVAC system. Theinvention is designed to be minimally invasive and work with a multitudeof unit styles and manufacturer brands and models. A new programmablecontroller having a central processor 3.10 and VFD 6 may be combined toform an efficiency enhancing controller (EEC) 8, are added to theexisting constant volume HVAC system roughly illustrated in FIG. 1.These components can be installed individually or as a single unit,discussed in further detail below.

The EEC is intended to be installed between the existing thermostaticdevice [9.1] and the heating and cooling equipment control terminations[9.3], e.g., low voltage terminal blocks. The VFD of the EEC isconnected to the fan motor [9.4],

The programmable controller, such as a Red Lion G303, and VFD, may beincorporated into a single unit for efficiency, such as a Yaskawa VI000Series. The single unit efficiency enhancing controller (EEC) 8, such asillustrated in FIG. 6, can receive and compare input signals, such asset point information or occupancy commands, and for relaying outputsignals to the fan motor (in operation, the ventilation mode) andcontrolling the heating equipment (in operation, the heating mode) andthe cooling equipment (in operation, the cooling mode) when ventilation,heating, or cooling is required (occupancy demands) or desired(programmed system targets).

Now also referring generally to FIGS. 7-13, the thermostatic device(thermostat) [9.1] is an electronic or mechanical device that is used tokeep the temperature of the space within an occupant defined range. Thethermostatic device may be a simple thermostat or a unitary controldevice referencing a space sensor. The thermostat may or may not havescheduling capabilities. Scheduling gives the thermostatic device theability to control at different temperature ranges during differenttimes of the day. This is most commonly used for night setback, anoperation where the defined control range of the thermostatic device isextended to increase energy savings when no occupants are in the space.The user defined range is often referred to as setpoints. When thetemperature of the air drops below the heating setpoint, thethermostatic device will send via the programmable controller anelectric signal to the HVAC equipment initiating a heat call. When thetemperature of air in the space rises above the cooling setpoint thethermostatic device will send via the programmable controller anelectric signal to the HVAC equipment initiating a cool call. Thethermostatic device, via the programmable controller and the VFD, willalso control the fan operation. The fan will run whenever the space isscheduled to be occupied. The fan will run whenever the thermostaticdevice initiates a signal for heating or cooling. Some thermostaticdevices will also have an occupancy contact that will send an electricsignal when the space is occupied.

The equipment low voltage terminal block [9.3] is where the thermostaticdevice makes electric connection with the HVAC equipment, typically at24 vac. The HVAC equipment processes the electrical signals receivedfrom the thermostatic device and makes determinations about mechanicallytreating the air with either heating or cooling to provide comfort asneeded.

As illustrated in FIG. 7, the EEC controller will receive heating,cooling, fan, and optional occupancy commands from the thermostaticdevice via discrete digital inputs, including the optional economizer.Digital inputs are only capable of representing two states: off or on.As required by the sequence defined below, the EEC will send low voltageelectric signals for heating or cooling to the equipment terminalconnections via discrete digital outputs. The EEC (through the VFD) willcontrol the fan speed by connecting directly to the line voltage inputof the existing fan motor. The fan motor is connected either via apulley or directly to a fan that is used to circulate air through thespace. The line voltage for the fan will be between 200-500 vac.

The central processor remains in an idle state until the existingthermostatic device [9.1] calls for the fan to come on. When thethermostatic device [9.1], via the EEC, sends an electric signal to turnthe fan on, the EEC (through the VFD) will control the fan to its newventilation speed. All low voltage signals from the thermostatic devicewill be processed by the EEC central processor. When the fan is enabled,the system will look to receive either a heat call or a cool call fromthe thermostatic device. The system also looks for an occupancy commandfrom the thermostatic device.

Now referring particularly to FIG. 8, ventilation mode occurs when thereis no need to heat or cool the space. During ventilation mode the fanwill run at a preset speed between 20-100%. The actual ventilation ratewill be determined on a case-by-case basis, but the typical ventilationrate will be a fan speed between 40-60%. The purpose is to find thelowest possible speed at which occupancy indoor air quality or coderequired ventilation rates can still be met. Such a reduction in the fanspeed results in energy savings compared with the status quo ofoperating the fan at 100% capacity during the ventilation mode.

The VFD changes the frequency of the power that is being supplied to themotor as a means to vary motor speed. Standard electrical frequency inthe United States is 60 Hz. A speed reference of 0-100% equals afrequency range of 0-60 Hz; at 60 HZ a motor is at maximum speed.

Acceptable ventilation may be determined by an occupancy sensing device.Occupancy can be determined by any device that can accurately measurehow many people are in a space; there are several methods of determiningoccupancy such as turn-styles or key card access systems. The device iscapable of accepting many different occupancy inputs, such as sensingcarbon dioxide levels, turn-styles, or key card access systems. But thepreferred method is the use of a CO₂ sensor, such as an AirtestEE80-2CS. Humans produce CO₂ as a byproduct of breathing. The ambientCO₂ is typically 450 PPM. Ventilation codes based on industry guidelinessuch as ASHRAE 2004 62.1 allows the use of CO₂ sensors to determinespace occupancy for ventilation purposes. The ventilation fan speed maybe set to keep the CO₂ level in the space between a code-permissible650-750 PPM while the outside air damper is at minimum position. Theventilation rate may need to be increased above this level in order tomaintain occupant indoor air quality by providing enough fresh outsideair to overcome issues like excessive odors and stale air.

Per code requirements, commercial buildings require fresh air forventilation. Ventilation is typically achieved through the outside airdamper of the economizer. A CO₂ sensor, as discussed above, may beinstalled to determine acceptable ventilation levels. The economizerwill operate at minimum position when there is no call for heating orcooling and the space is occupied. A minimum position typically will beset to 5%. A mixed air temperature chart, such as illustrated in FIG.16, may also be used to set the minimum position.

At setup, the installing technician will measure return air, outsideair, and mixed air. Return air is the air coming back from the space.Outside air is the ambient condition surrounding the unit. Mixed air iswhere the return air and outside air are mixed together; it is after thedampers and before any heating or cooling coils. Technicians will usethe mixed air chart and the measured values to establish the appropriateoutside air damper position. The economizer position as expressed in apercentage, as it pertains to the outside air is damper is a referenceof percentage open. The economizer position as expressed in percentages,as it pertains to the return air damper is a reference of percentageclosed. When the minimum economizer position is at 5% the outside airdamper is 5% open and the return air damper is 5% closed (or 95% open).If damper appears to be all of the way closed, but the measurements showair leakage is greater than 5%, the damper will be left in this closedposition for minimum ventilation. Air leakage is the ability of theoutside air to infiltrate past a closed damper and influence thetemperature of the mixed air.

If the CO₂ in the space rises above a selected level, such as 1200 PPMas measured by the CO₂ sensor, the economizer will be modulated open toattempt to keep the CO₂ levels at the selected level. Modulate means thecontrol output (in this case the economizer configuration) is variedthroughout a control range to match the needs of the space. The CO₂control will be based on a PID (proportional plus integral derivative)loop to continuously calculate the percentage of ventilation that isneeded to maintain ventilation levels and take corrective action asneeded to reach the setpoint. The proportional effect is how far thevalue is away from the setpoint. The integral effect is how long (inseconds) the deviation from the setpoint has existed. The derivativeeffect, though rarely used, considers sudden variations. All of thesevalues are combined to determine the output level needed to satisfy thesetpoint.

If the damper reaches 100% for a selected period of time, e.g., 10minutes, and the CO₂ level is greater than a selected level ofconcentration, e.g., 1500 PPM, the fan speed will change to meet theincrease in ventilation needs. The fan speed will ramp at a selectablerate, e.g., 1% every 5 seconds) until the CO₂ level drops below theselected concentration, e.g., 1450 PPM. If the ventilation rate startsto drop below a selected concentration, e.g., 1350 PPM, the fan willramp down at a selectable rate (such as already mentioned above) untilthe fan is at its ventilation speed.

Now referring particularly to FIGS. 9 and 10, when the central processorreceives a signal from the thermostatic device that heat is needed andthe thermostatic device does not indicate occupancy, the EEC is eitherin a night heating or morning warm-up mode, and the outside air damperwill remain closed. This function known as “unoccupied damper control”may not be implemented on all units because not all thermostatic deviceshave an occupancy output.

“Single stage equipment” are units that have only one stage ofmechanical heating and/or cooling. Multiple stage equipment has multiplemeans to mechanically heat and/or cool the air. It is common to havebetween two and four stages on multi-stage cooling equipment. Each stageof cooling adds additional capacity, until the unit reaches its maximumcapacity with all stages engaged. In heating, two stages are most commonfor multi-stage equipment. Each stage of heating adds additionalcapacity until the unit reaches its maximum capacity with all stagesengaged.

In a single stage unit, on a signal for cooling from the thermostaticdevice, the fan will run at a reduced speed, typically at 90% of maximumspeed, or no less than the manufacturer's minimum recommended airflow.This reduction in fan speed results in energy savings compared with thestatus quo of operating fans at 100% during the cooling mode. The VFDwill adjust the frequency of the line power supplied to the motor toachieve the desired speed.

In multistage units, the fan may be controlled under one of twoscenarios: 1) “consistently reduced” (e.g., 90%); or 2)“ramp-with-demand.” In the consistently reduced scenario, the fan willoperate at 90% speed whenever the thermostatic device sends a signal forany stage of cooling. In a “ramp-with-demand” scenario, the fan speedwill increase (ramp) as the unit is required to produce additionallevels of cooling (demand). Each individual stage of the multistageequipment will add to the capacity (measured in tons) that the unit isproducing. During initial installation, the field programmer will entera value into the EEC central processor for tons per stage. The EECcentral processor will control the fan speed to maintain no less thanthe manufacturer's recommended airflow (e.g., 360 CFM/per ton). Forexample, if there are four stages and 20 total tons of capacity, thetechnician would enter 5 tons per stage. If two stages are engaged, thenthe unit would modulate the fan to maintain 3600 CFM based on industrystandard minimums of 360 CFM per ton. In the ramp with demand scenario,an air flow sensor will be installed in the supply air duct to measureair flow. Air flow will be measure in velocity (feet/minute), and thecentral processor will convert the signal to volume (CFM). The EECcentral processor may use a PID control loop (as described above) tomaintain a necessary fan speed to meet the CFM requirements. The VFDwould adjust the frequency of the line power supplied to the motor toachieve the desired speed. Collectively, these changes from status quofan speed control result in valuable energy savings.

Now referring also to FIG. 11, the EEC will determine if the unit shouldoperate in economizer mode when the thermostatic device sends a signalfor cooling. Economizer mode is when the HVAC equipment uses suitableoutside air to treat the space being conditioned. In economizer mode theoutside air damper will open and the return air damper will close asnecessary; outside air will be provided to the space in an attempt tosatisfy the cooling demand. If the outside air is unsuitable for coolingthen the economizer damper will be set to its minimum position andmechanical cooling will be enabled. If the thermostatic device sends asignal for cooling in an unoccupied mode, and the outside air issuitable for free cooling, the economizer will use outside air tosatisfy the space demand, and mechanical cooling will be locked out fromoperating. If the thermostatic device sends a signal for cooling in anunoccupied mode and the outside air is not suitable for free aircooling, the economizer will remain closed and mechanical cooling willbe used to satisfy the space. One of three variables will be used by theEEC to determine if the outside air is suitable for free cooling. Thesevariables are enthalpy, temperature, or dew point.

When the economizer is enabled it will be modulated to maintain a 55° F.supply air temperature. A PID loop will control the output that isconnected to an economizer actuator. The outside air damper will beopened proportionately to meet the demand required to maintain thesupply air setpoint. An actuator is a motor that is used to controldamper position. An analog output will be used to control the actuatorposition. An analog output is the variable electric signal generated bythe central processor in response to a command. Commonly, a command of0-100% will be converted to an electric signal of 0-10 vdc.

In the event that the outside air is determined to be incapable ofadequately cooling the space, a differential economizer control strategymay be utilized. Mechanical cooling is activated and the economizer isnow controlled based on one of three comparative strategies:differential enthalpy, differential temperature, or differential dewpoint.

Differential enthalpy requires the following sensors: outside airenthalpy and return air enthalpy. Enthalpy, measured in BTU/lb of air,is a measurement of the total heat quantity in the air. Enthalpy is acombination of the temperature and humidity in the air. Enthalpy isparticularly useful in areas with high humidity. Enthalpy takes intoconsideration the latent heat in the moisture that humidity adds to theair being treated. The enthalpy sensors, such as Honeywell C7400A1004,are connected to the analog inputs of the EEC. The analog input canaccept either a varying voltage, current, or resistive signal from afield sensor. The analog input reads the changing electric value andconverts it to useable data. For example, in the case of the enthalpysensor, a range of 15-40 BTU/lb of air has an electric signal of 4-20mA. Differential enthalpy involves the logical comparison of theenthalpy of the outside air and the enthalpy of the return air. If theoutside air has a lower heat quantity than the return air, the outsideair is the preferred source for cooling operations and economizer modeis enabled. Less energy is required to mechanically cool the outside airbecause it has a lower heat quantity than the return air.

In areas of low humidity, differential temperature economizer controlmay be implemented. The concept of differential temperature is similarto enthalpy, but differential temperature does not factor in the latentheat in the moisture of the air. In the case of differentialtemperature, a return air temperature sensor and an outside airtemperature sensor will be connected to the EEC analog inputs.Differential temperature involves the logical comparison of thetemperature of the outside air and the temperature of the return air.The lower of the two temperatures will determine whether outside air orreturn air is the preferred source for cooling operations and economizermode is enabled, resulting in lower energy consumption.

Differential dew point is the final changeover method. For dew pointeconomizer control temperature and humidity sensors will sense both thereturn air and outside air conditions and be connected to the EEC analoginputs. The EEC will calculate dew point based on the temperature andhumidity readings. Differential dew point involves the logicalcomparison of the return air and outside air values. If the calculateddew point of the outside air is less than calculated dew point of thereturn air, the outside air is the preferred source for coolingoperations and economizer mode is enabled. It will require less energyto mechanically cool the outside air because it has a lower dew pointthan the return air.

The EEC will control the mechanical cooling functions, namely, the HVACequipment's ability to mechanically lower the temperature of air in thebuilding space. In most systems mechanical cooling will be achievedthrough a compressor and refrigeration cycle. Mechanical cooling will beenabled when there is a signal from the thermostatic device and freecooling is not available, or if the economizer mode alone is unable tokeep up with the demand. If the economizer is fully open for aselectable period of time (e.g., ten minutes) and the return airtemperature or enthalpy has not decreased by a selectable percentage(e.g., 5%) mechanical cooling will be enabled. Or, if the economizer isfully open for a selectable period of time (e.g., 15 minutes) and thespace temperature setpoint remains unsatisfied, mechanical cooling willbe enabled. The present invention may utilize the practice ofsimultaneous economizer and mechanical cooling operation known as“integrated economizer” until the outside air is determined to beunsuitable. Once mechanical cooling has been initiated, each stage ofmechanical cooling must run for a selected minimum amount of time,typically 3-5 minutes. Once it has been turned off, each stage ofcooling must remain off for a select minimum amount of time, typically3-5 minutes, before it can be turned back on.

Referring again to FIG. 9, on HVAC equipment with multiple stages ofcooling, the first stage of cooling will be initiated when mechanicalcooling is needed. If the first stage of cooling is still on after aselected amount of time (e.g., 5 minutes), and return air temperature orenthalpy has not decreased by a selected percentage (e.g., 5%), thesecond stage of cooling is turned on. If the first stage of cooling ison for a selected amount of time (e.g., 10 minutes), the second stage ofcooling will be turned on. This process will repeat for all subsequentstages of cooling until all stages of cooling are on, or the spacecooling demands have become satisfied.

Referring again to FIG. 10, the ECC will control the mechanical heatingfunctions. Mechanical heating refers to any method used by the HVACequipment to mechanically raise the temperature of air in the space. Inmost systems mechanical heating will be achieved through gas heating,electric strip heating, or compressor and refrigeration cycle (heatpump). In a single stage unit, when mechanical heating is needed theonly stage of heating will turn on. When the heating is on, thetemperature of the air being supplied to the space will increase and thespace will heat up.

On HVAC equipment with multiple stages of heat, when mechanical heatingis needed, the first stage of heating will come on. If the first stageof heating is still on after a selected amount of time, e.g., 5 minutes,and the return air temperature or enthalpy has not increased by aselected percentage, e.g., 5%, the second stage of heating is turned on.If the first stage of heating is on for a selected amount of time, e.g.,10 minutes, the second stage of heating will be turned on. This processwill repeat for all subsequent stages of heating until all stages ofheating are on, or the space becomes satisfied. Once heating has beeninitiated, each stage of heating must run for a selected minimum ofamount of time, typically 3-5 minutes. Once it has been turned off, eachstage of heating must remain off a selected minimum amount of time,typically 3-5 minutes, before it can be turned back on.

Referring now to FIGS. 12 and 13, the invention may be equipped with anadvanced diagnostic and fault detection capability. For the purposes offault detection, a discharge air temperature sensor may be added to eachindividual HVAC system. There are three fault processes that arecalculated: fan fault [11.1], heat/cool (temperature-based) fault[11.4], and an energy consumption (kWh) fault [11.8]. The fan [11.1] andtemperature [11.4] faults are interconnected. The system will first runthrough the fan logic, and then run through the heat/cool logic. Theenergy consumption fault [11.8] is independent, and runs continuouslywhile the unit is in operation.

The fan fault [11.1] is initiated whenever there is a call for the fanto operate [3.4]. The EEC processor first verifies that the fan statusis proven. If the fan status does not prove within a select amount oftime (e.g., 30 seconds) from the fan “on” command [3.4], the “fanrunning” fault [11.2] will trigger a fan fault [11.12]. If the “fanrunning” fault [11.2] does not exist, the system will then analyze themotor speed [11.3]. If the system is not calling for heat [3.2], cool[3.3], or additional ventilation [4.7], the fan should be operating atthe ventilation speed setpoint [4.4]. If the fan is not at the correctventilation speed [11.3] it will trigger a fan fault alarm [11.2].

Assuming there are no fan faults [11.1] the system will begin to analyzethe temperatures for heat/cool based faults [11.4]. Depending on themode of operation (heat [3.2] or cool [3.3]) the system will look for adrop or a rise in the discharge air temperature [11.9]. If the systemdoes not see a change in discharge temperature [3.9] after a selectedamount of time (e.g., 10 minutes) the system will initiate a heat/coolfault alarm [11.14]. If the system has additional stages of heating[6.4] or cooling [5.11] the system will look for an additional change inthe discharge temperature [3.9]. If there is not a change in temperaturewhen additional stages are enabled the system will initiate a heat/coolfault alarm [11.14], If the heating call [3.2] or cooling call [3.3]exists without interruption for more than a select period of time,(e.g., 30 minutes), a “time-in-mode” fault [11.7] will trigger theheat/cool alarm [11.14]. If none of the previous conditions exist, thesystem will not have a heat/cool fault condition [11.14].

The energy consumption fault circuit [11.10] will run whenever the unitis powered up. The consumption fault detection logic is set to gathersystem data at preset intervals. The intervals can be adjusted by theprogrammer in the field. The fault detection comparisons will start whenthe when the designated time interval has elapsed [12.1]. The systemwill gather the average outside air temperature, heat mode runtime, coolmode runtime, and the ventilation mode runtime [12.2]. The system willthen scan an internal database [12.4] for a matching sample time of dayand outside air combination. If the matching combination does not exist,the information will be added to the database [12.9]. If the combinationdoes exist in the database, the controller will first look to see ifthere are a sufficient number of values (e.g., 5) for the combination[12.3]. If there are a minimum number of stored values for the range,the controller is deemed to have enough historical data to provide avalid comparison. The controller will compare the sampled energyconsumption amounts [12.2] against the items stored in the database. Ifthe consumption is not within the normal range of values, then an energyconsumption fault will be triggered. If the value is within the normalrange, then no fault will be triggered. The controller will analyze forcooling consumption [12.5], heating consumption [12.6], and ventilationconsumption [12.8]. Each mode is capable of issuing a correspondingfault or no fault condition [12.10-12.15].

Energy conservation is achieved through this fault detection andreporting feature by alerting operators when the unit is using excessiveenergy. This may be due to inappropriate changes in the unit's operatingschedule, low refrigerant charge, or other mechanical issues.

For the purpose of remote communication, monitoring and data collectionthe present method and EEC apparatus may be utilized in a networkedversion (as opposed to a stand alone version) schematically representedin FIGS. 14 and 15. A central processor 11 (e.g., a computer), a modem12, or other communication means are added to each networked system. Thecentral processor 11 is connected in a wired or wireless configurationto each EEC/controller and gathers data from each device.

The EEC will be manufactured and applied in different embodiments tomatch the individual equipment and building space needs. One embodimentof the EEC consists of fan speed control, where the fan operates atdifferent speeds depending upon whether there is a call for heating orcooling or if the system is in the ventilation mode. Another embodimentof the EEC consists of fan speed control based on a need for heating,cooling, and occupancy based ventilation, where the ventilation needsare based on an input form an occupancy sensor. Another embodiment ofthe EEC controls the fan speed based on heating, cooling, ventilation,and advanced economizer strategies including unoccupied damper control,differential change-over, and integrated economizer control. Theindividual versions of the EEC can be implemented in a networked orstand alone version and may include the capability for fault detection.

All the disclosed embodiments of the invention disclosed herein can bemade and used without undue experimentation in light of the disclosure.Although the best mode of carrying out the invention contemplated by theinventors is disclosed, practice of the invention is not limitedthereto. Accordingly, it will be appreciated by those skilled in the artthat the invention may be practiced otherwise than as specificallydescribed herein.

The individual components need not be formed in the disclosed shapes, orcombined in the disclosed configurations, but could be provided invirtually any shapes, and/or combined in virtually any configuration.Further, the individual components need not be fabricated from thedisclosed materials, but could be fabricated from virtually any suitablematerials.

Variations may be made in the steps or in the sequence of stepscomposing methods described herein. All the disclosed elements andfeatures of each disclosed embodiment can be combined with, orsubstituted for, the disclosed elements and features of every otherdisclosed embodiment except where such elements or features are mutuallyexclusive.

It will be manifest that various substitutions, modifications, additionsand/or rearrangements of the features of the invention may be madewithout deviating from the spirit and/or scope of the underlyinginventive concept. It is deemed that the spirit and/or scope of theunderlying inventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” and/or “stepfor.” Subgeneric embodiments of the invention are delineated by theappended independent claims and their equivalents. Specific embodimentsof the invention are differentiated by the appended dependent claims andtheir equivalents.

What is claimed is:
 1. A system comprising: a variable frequency driveconfigured to drive a fan motor of an HVAC system within a range of fanmotor speeds to ventilate an indoor space, the HVAC system having acooling assembly that includes at least one of an economizer or acompressor; and a controller configured to (i) communicate with thevariable frequency drive, (ii) receive signals corresponding to whetherthe indoor space is less than fully occupied, (iii) control the variablefrequency drive to reduce a speed of the fan motor based on the receivedsignals, (iv) and determine at least one of a fan fault, atemperature-based fault, or an energy consumption fault.
 2. The systemrecited by claim 1, wherein the controller is further configured tocommunicate with a thermostatic device and control the cooling assemblybased on communication with the thermostatic device.
 3. The systemrecited by claim 1, wherein the HVAC system includes a heating assemblyand the controller is further configured to communicate with athermostatic device and control the heating assembly to heat the indoorspace.
 4. The system recited by claim 1, wherein the controller isfurther configured to determine whether the indoor space is less thanfully occupied and control the variable frequency drive to reduce thespeed of the fan motor in response to determining that the indoor spaceis less than fully occupied.
 5. The system recited by claim 1, whereinthe controller is further configured to determine the energy consumptionfault by: determining an outside air temperature, a heat mode runtime, acool mode runtime, and a ventilation mode runtime at preset intervals;determining an actual energy consumption of the HVAC system; accessing adatabase that stores historical data correlating time of day data andoutside air temperature data with energy consumption data of the HVACsystem to determine a normal energy consumption range for the HVACsystem; comparing the actual energy consumption of the HVAC system withthe normal energy consumption range; and determining that the energyconsumption fault exists in response to the actual energy consumptionbeing outside of the normal energy consumption range.
 6. The systemrecited by claim 5, wherein the controller is further configured togenerate an alert in response to determining that the energy consumptionfault exists.
 7. The system recited by claim 1 further comprising acarbon dioxide sensor, wherein the controller is further configured toreceive the signals from the carbon dioxide sensor.
 8. The systemrecited by claim 7, wherein the controller is further configured todetermine whether the indoor space is less than fully occupied based onthe signals from the carbon dioxide sensor and control the variablefrequency drive to reduce the speed of the fan motor in response todetermining that the indoor space is less than fully occupied.
 9. Thesystem recited by claim 1, wherein the controller is configured todetermine the fan fault.
 10. The system recited by claim 1, wherein thecontroller is configured to determine the temperature-based fault. 11.The system recited by claim 1, wherein the controller is configured todetermine the energy consumption fault.
 12. A method comprising:receiving, with a controller of an HVAC system for an indoor space,signals corresponding to whether the indoor space is less than fullyoccupied, the HVAC system having a cooling assembly that includes atleast one of an economizer or a compressor; controlling, with thecontroller, a variable frequency drive that drives a fan motor of theHVAC system within a range of fan motor speeds to ventilate the indoorspace by reducing the speed of the fan motor based on the receivedsignals; and determining, with the controller, at least one of a fanfault, a temperature-based fault, or an energy consumption fault. 13.The method recited by claim 12, further comprising communicating, withthe controller, with a thermostatic device and controlling, with thecontroller, the cooling assembly based on the communication with thethermostatic device.
 14. The method recited by claim 12, wherein theHVAC system includes a heating assembly, the method further comprisingcommunicating, with the controller, with a thermostatic device andcontrolling, with the controller, the heating assembly to heat theindoor space.
 15. The method recited by claim 12, further comprisingdetermining, with the controller, whether the indoor space is less thanfully occupied and controlling, with the controller, the variablefrequency drive to reduce the speed of the fan motor in response todetermining that the indoor space is less than fully occupied.
 16. Themethod recited by claim 12, wherein the controller determines the energyconsumption fault by: determining an outside air temperature, a heatmode runtime, a cool mode runtime, and a ventilation mode runtime atpreset intervals; determining an actual energy consumption of the HVACsystem; accessing a database that stores historical data correlatingtime of day data and outside air temperature data with energyconsumption data of the HVAC system to determine a normal energyconsumption range for the HVAC system; comparing the actual energyconsumption of the HVAC system with the normal energy consumption range;and determining that the energy consumption fault exists in response tothe actual energy consumption being outside of the normal energyconsumption range.
 17. The method recited by claim 16, furthercomprising generating, with the controller, an alert in response todetermining that the energy consumption fault exists.
 18. The methodrecited by claim 12, further comprising receiving, with the controller,the signals from a carbon dioxide sensor.
 19. The method recited byclaim 18, further comprising determining, with the controller, whetherthe indoor space is less than fully occupied based on the signals fromthe carbon dioxide sensor and controlling, with the controller, thevariable frequency drive to reduce the speed of the fan motor inresponse to determining that the indoor space is less than fullyoccupied.
 20. The method recited by claim 12, wherein the controllerdetermines the fan fault.
 21. The method recited by claim 12, whereinthe controller determines the temperature-based fault.
 22. The methodrecited by claim 12, wherein the controller determines the energyconsumption fault.
 23. A system comprising: a controller configured to(i) communicate with a variable frequency drive that is configured todrive a fan motor of an HVAC system within a range of fan motor speedsto ventilate an indoor space, the HVAC system having a cooling assemblythat includes at least one of an economizer or a compressor, (ii)receive signals corresponding to whether the indoor space is less thanfully occupied, (iii) control the variable frequency drive to reduce aspeed of the fan motor based on the received signals, (iv) and determineat least one of a fan fault, a temperature-based fault, or an energyconsumption fault.
 24. The system recited by claim 23, wherein thecontroller is further configured to communicate with a thermostaticdevice and control the cooling assembly based on communication with thethermostatic device.
 25. The system recited by claim 23, wherein theHVAC system includes a heating assembly and the controller is furtherconfigured to communicate with a thermostatic device and control theheating assembly to heat the indoor space.
 26. The system recited byclaim 23 further comprising a carbon dioxide sensor, wherein thecontroller is further configured to receive the signals from the carbondioxide sensor.
 27. The system recited by claim 26, wherein thecontroller is further configured to determine whether the indoor spaceis less than fully occupied based on the signals from the carbon dioxidesensor and control the variable frequency drive to reduce the speed ofthe fan motor in response to determining that the indoor space is lessthan fully occupied.
 28. The system recited by claim 23, wherein thecontroller is configured to determine the fan fault.
 29. The systemrecited by claim 23, wherein the controller is configured to determinethe temperature-based fault.
 30. The system recited by claim 23, whereinthe controller is configured to determine the energy consumption fault.